[Feature] add simple FIFO capabilities

[matthewfcarlson]

This adds rudimentary FIFO capabilities to this library. Namely, turning it off and on, toggling the different modes, and checking if there is data in the fifo.

There's a new example that shows how to use this particular library. I've only tested it with I2C but based on my understanding, SPI shouldn't apply here since we aren't doing burst writes or reads.

Fixes #29